I have a program that scans and updates its results to std out every second. I would like to capture its output for further processing, but there is a catch. I would like to capture a snapshot after about 15 seconds as the results become more accurate and close the program.
Obviously I can simply use > temp_file which I can use by grabbing the last n lines, and close the program after 15 seconds but surely there is a better way?
Just looking for a general idea to get me in the right direction.
TLDR: Is there a way to capture the std out of a program directly before it closes?
Last edited by Riker1204; 03-11-2017 at 06:31 PM..
I have a program that scans and updates its results to std out every second. I would like to capture its output for further processing, but there is a catch. I would like to capture a snapshot after about 15 seconds as the results become more accurate and close the program.
Obviously I can simply use > temp_file which I can use by grabbing the last n lines, and close the program after 15 seconds but surely there is a better way?
Just looking for a general idea to get me in the right direction.
TLDR: Is there a way to capture the std out of a program directly before it closes?
Code:
#!/bin/bash
program > program.log 2>&1 &
pid=$!
for s in {1..15}
do
sleep 1
done
kill $pid
Thank you for the input, but this will still capture output from beginning to end of execution.
Is there a way to dynamically change a File Descriptor after 15 seconds, say std out to > /dev/null for first 15s then std out to > FILE && close program?
Last edited by Riker1204; 03-12-2017 at 01:45 AM..
Reason: clarity
In bash you could have process substitution manage a named pipe for you. Below I duplicate this with exec onto file descriptor 7.
You can then simply read and discard from this file descriptor for 15 seconds,. If you can be sure of a maximum amount of data going to be sent (eg here we are limited to 10000 characters) you can simplify this to a single read statement:
Code:
#!/bin/bash
exec 7< <(./program 2>&1 )
# Discard first 15 seconds of data (limit is 10000 characters)
read -u 7 -t 15 -N 10000 discard
# Now you can read line you are interested in
read -u 7 -t 3 line
or without a size limit just read lines for 16 seconds, keeping the last read:
Code:
#!/bin/bash
exec 7< <(./program 2>&1 )
# Read data for 16 seconds
for((i=SECONDS+16;SECONDS<i;))
do
read -u 7 -t $((i-SECONDS)) line
done
# At this point, $line will be last line output after 16 secs
Edit: Solution using coprocesses (required bash4). we run the process, discard first 10,000 characters or 15 seconds of input and then read the next line. This will also kills the process once we have the required result:
Code:
coproc { ./program 2>&1 ; }
#discard 15 seconds or 10,000 characters of input (whichever is the first)
read -u ${COPROC[0]} -t 15 -N 10000 discard
# wait up to 3 seconds for the next line of output
read -u ${COPROC[0]} -t 3 line
# kill process
kill $COPROC_PID 2> /dev/null
if [ -z "$line" ]
then
echo "timeout - no output line after discarding early stuff"
else
echo "Last line: $line"
fi
This could also be coded using named pipes in other shell versions if needed.
Last edited by Chubler_XL; 03-12-2017 at 08:28 PM..
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